The present invention relates to a method and a device for the recovery of desired fluid hydrocarbon from an underground porous formation. The typical porous formation to which this method and device relate is a porous oil and gas bearing sand entrapped underground between a fluid impermeable cap rock above and a fluid impermeable stratum below. The typical desired fluid is liquid of gaseous hydrocarbon. The present invention relates to a method and a system which solves or avoids problems associated with prior art methods and systems used to recover desired fluid hydrocarbons, such as oil or gas, from oil and gas bearing sands, which prior art is characterized by tunneling within or below the porous formation and drilling into the sands so that the desired fluid drains by the force of gravity into collection pits located on the floor of the tunnel.
Prior art methods and systems for using mine shafts or tunnels with oil drain pits for collecting oil drained from oil sands by the force of gravity have typically been called "oil-mining" systems or methods. In one early method, tunnels were driven horizontally through the impermeable cap rock above the oil bearing sand and square pits were dug vertically through the tunnel floor to the oil bearing sands a few feet below. The oil drained into these pits and was lifted periodically by a pneumatic device into a pipeline extending to surface tanks. This system was used in the Pechelbronn field near Hanover, Germany and is disclosed in G. S. RICE, U.S. BUREAU OF MINES.
Another variation of this method is known as the Ranney oil-mining system and is disclosed in L. C. UREN, PETROLEUM PRODUCTION ENGINEERING: OIL FIELD EXPLOITATION, 3d Ed. McGRAW-HILL (1953). In this system mine galleries or tunnels are driven in impermeable strata above or below the porous formation of oil bearing sand and holes are drilled into the porous formation at short intervals along these galleries. Fluid is withdrawn through pipes sealed into the drilled holes and is pumped to the surface through a system of drain pipes in the galleries.
Another method which has been proposed for mining oil from partially drained oil bearing sands involves drilling a vertical mine shaft through the porous formation and drilling long slanting holes radially in all directions from the shaft bottom into the oil sands. The oil was to drain from the sand through the radial slant holes into a pit or sump at the bottom of the shaft and was to be pumped to the surface.
There are problems associated with these prior art oil-mining systems. For example, where high pressure gases may be present in the porous formation the prior art methods may be ineffective because either the gas will escape directly into the tunnels, galleries, or shafts or the gas will force itself directly into the collection pipe system, thereby leaving the liquid unrecovered in the porous formation. Another problem associated with reservoirs in which both gas and liquid hydrocarbons exist in that a mixture of gas and liquid will be recovered in the pipe system, thereby creating difficulties both in pumping the mixture to the surface and in separating the mixture under conditions existing in collection vessels at the surface. Typically pumps are designed to pump either liquid or gas alone and do not work efficiently when pumping a mixture of both. Also, separation of the hydrocarbons at the surface may require complex procedures and may result in dangerous chemical reactions, which chemical reactions would not occur if the separation of the liquid from the gas was accomplished under the conditions existing in the underground formation.
Further problems associated with prior art oil-mining systems occur when undesired fluids, such as water or brine, exist in the porous formation. The prior art systems essentially drain all fluids indiscriminately. Pumping or transporting the entire mixture requires the expenditure of energy in pumping the undesired fluids to the surface. Also the prior art systems involve the expense and complication of separating the desired fluid hydrocarbon from the undesired fluid when the mixture reaches the surface.